Noticeable temp gradient in passive home – suggestions to mitigate?
Hi all,
I live in a 2k (1k per floor) square foot home built to passive house standards in Vermont. My first floor is a fairly open rectangle with a Mitsubishi mini split on the west wall. On the opposite side of the floor is our living room and couch separated by a kitchen. Some days, like today, there is a change of up to 7 degrees (measured w IR gun) from he heater to the living area. The outside temp is 20f.
We should have centralized the HP but opted not to place in our centrally located kitchen. I did expect our heat recovery (CERV) would move air around the house better but am not convinced it does (I will start some experiments).
Have people experienced similar issues and if so how have you remedied? I think I may install a wall mounted thermo by the couch which won’t help the gradient but will ensure I’m getting the right temp where I most often sit. Looks like one option is Mitsubishi MKH1.
If if people have experienced similar issues what have you done to help? Any other recommendations for temp control besides MKH1? Any suggestions for experiments I should conduct?
Todd
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Replies
Consider open (non-ducted) fans to move lots of air between rooms. Up high, where it hopefully won't cause a noticeable draft.
Yup...fan.
I have a similar setup, and I'm surprised you have that issue. My heat pump is on the north wall, so I guess that's more centralized than if it was on the west wall. But my main floor is also 1600 square feet. The only rooms that are noticeably cooler sometimes are the bathroom and the utility room, and even at that it's not more than 2degF. How well is your house insulated, what's the blower door reading and what kind of windows? I guess it's just academic, but I'm curious. I agree that the most obvious solution is a fan or two.
As for the ERV moving air around, it's well known that the amount of air they move has a negligible effect on movement of heat. Feel free to experiment, but you're kind of reinventing the wheel by doing it.
Thanks Trevor. Two layers of rockwool R-23 each, r-80 attic. Ach50 score of .3. Schuco living 82 (triple paned w custom insulated window bucks).
How is your air circulated or is it? The layout is slightly more complex than I first described, the air from the HP must go down a small entry hall and past our kitchen then the couch is slightly around the corner.
I did turn on the CERV recirculation this morning and also the sun has come up to add some solar gain, currently reading around 71-72 in the entry by HP and 69 at the couch.
The air is only circulated by the throw of the indoor head, convection currents, diffusion, etc.
The less open layout is most likely the difference maker. I'm still surprised by the magnitude of difference, but it makes more sense now.
Getting some more air mixing in the house is the first step. Just watch how you do it, moving air is never free, something like and HRV/ERV blower uses a lot of power to move very little BTU when in circulation mode. For example if you have a 5F delta between the two sides, a 100CFM blower would only move 500btu of heat while consuming around 60W.
Even the best windows are pretty awful compared to even code min walls. If find that if I turn off my floor heat and only use the mini split, the house is still comfortable but quickly becomes cool by the windows. The extra bit of heat there makes a big difference for comfort.
You could try putting a small panel heater there. It doesn't need to add a lot of BTUs to the house to make a big difference in comfort. Just need enough heat to reverse the convective currents there.
> becomes cool by the windows
A good reminder that heat source location (even within a room) does matter.
Hi TJ,
Did you ever figure out a solution to this? Also, how do you like your CERV in general?